Carbon dioxide is a greenhouse gases produced during the combustion of coal power plants. Its effect on climate change has led to international political action aimed at limiting the amount of carbon dioxide produced around the world. The United States is presently considering a national emission trading program, under which industries with higher emission levels of greenhouse gases can buy “emission credits” from others that are not emitting their allotted levels of greenhouse gases.
Thus, there is growing political will to reduce the levels of carbon dioxide produced by coal-fired power plants. New methods that to reduce the emissions of carbon dioxide are needed.
The present invention chemically converts the carbon dioxide to a solid, eliminating its emission during the process of converting coal to steam or electricity. It is different from most if not all existing methods, which treat the carbon dioxide after it is emitted from the conversion process. For example, one well known process involves sequestration of the gaseous carbon dioxide produced by coal-fired and other power plants by injection in underground reservoirs.
Post process solidification by a different process is also known. For example, one existing method of carbon dioxide sequestration involves reacting the carbon dioxide discharged from the combustion process with large quantities of calcium oxide and magnesium oxide, then burying the resulting carbonates. Treating carbon dioxide after it is emitted from the process eventually leads to releasing some of it to the environment during compression, transportation, treatment and disposal.
The prior art includes conversion of the coal to methane in a gasification process followed by capturing the produced carbon dioxide with calcium oxide. The calcium oxide is calcined from mined mineral. However, one of the key technical development issues with this proposed method is a fuel cell that is tolerant of sulfur compounds released by the coal gasification, and, as such, the fuel cell may be more difficult to develop than fuel cells fired with methane, i.e., natural gas (although natural gas also contains minute quantities of sulfur). The present invention minimizes the sulfur compounds and other contaminants by forming solid ash.
Another issue with this prior art is the possibility of inefficient heat transfer between many steps in this complex system, which may sharply reduce the feasibility of this cycle. Additionally, since no large central station power plants with methane fuel cells are in existence, the probability of developing even a full scale prototype plant for this much more complicated coal fired system in the near future is very small, and the possibility of building enough power plants of this type to meaningfully reduce carbon dioxide emissions is even smaller.